Conventional ultrasound imaging systems comprise an array of ultrasonic transducer elements which are used to transmit an ultrasound beam and then receive the reflected beam from the object being studied. For ultrasound imaging, the array typically has a multiplicity of transducer elements arranged in a line and driven with separate voltages. By selecting the time delay (or phase) and amplitude of the applied voltages, the individual transducer elements can be controlled to produce ultrasonic waves which combine to form a net ultrasonic wave that travels along a preferred vector direction and is focussed at a selected point along the beam. Multiple firings may be used to acquire data representing the same anatomical information. The beamforming parameters of each of the firings may be varied to provide a change in maximum focus or otherwise change the content of the received data for each firing, e.g., by transmitting successive beams along the same scan line with the focal point of each beam being shifted relative to the focal point of the previous beam. By changing the time delay and amplitude of the applied voltages, the beam with its focal point can be moved in a plane to scan the object.
The same principles apply when the transducer probe is employed to receive the reflected sound in a receive mode. The voltages produced at the receiving transducer elements are summed so that the net signal is indicative of the ultrasound reflected from a single focal point in the object. As with the transmission mode, this focused reception of the ultrasonic energy is achieved by imparting separate time delay (and/or phase shifts) and gains to the signal from each receiving transducer element.
Such scanning comprises a series of measurements in which the steered ultrasonic wave is transmitted, the system switches to receive mode after a short time interval, and the reflected ultrasonic wave is received and stored. Typically, transmission and reception are steered in the same direction during each measurement to acquire data from a series of points along an acoustic beam or scan line. The receiver is dynamically focussed at a succession of ranges along the scan line as the reflected ultrasonic waves are received.
FIG. 1 depicts an ultrasound imaging system consisting of four main subsystems: a beamformer 2, processors 4 (including a separate processor for each different mode), a scan converter/display controller 6 and a kernel 8. System control is centered in the kernel, which accepts operator inputs through an operator interface 10 and in turn controls the various subsystems. The master controller 12 performs system level control functions. It accepts inputs from the operator via the operator interface 10 as well as system status changes (e.g., mode changes) and makes appropriate system changes either directly or via the scan controller. The system control bus 14 provides the interface from the master controller to the subsystems. The scan control sequencer 16 provides real-time (acoustic vector rate) control inputs to the beamformer 2, system timing generator 24, processors 4 and scan converter 6. The scan control sequencer 16 is programmed by the host with the vector sequences and synchronization options for acoustic frame acquisitions. The scan converter broadcasts the vector parameters defined by the host to the subsystems via scan control bus 18.
The main data path begins with the analog RF inputs to the beamformer 2 from the transducer 20. The beamformer 2 outputs two summed digital baseband I,Q receive beams. The I,Q data is input to a processor 4, where it is processed according to the acquisition mode and output as processed vector (beam) data to the scan converter/display processor 6. The scan converter accepts the processed vector data and outputs the video display signals for the image to a color monitor 22.
The task of the ultrasound transducer in the diagnostic imaging system is to provide a stable, specified level of performance for transduction of electrical energy into acoustic energy and vice versa. Classically, the transduction process is established through the use of a piezoelectric sensor which is designed to function optimally on one type of imaging system. This is required because the system parameters of number of elements and aperture size are fixed by the system designers, not the transducer engineers.
To meet the image size or field of view requirements for a particular application, multiplexers are conventionally incorporated into probes, allowing the use of a transducer with more elements than the system has channels. Because the multiplexer allows the use of probes with more elements than system channels, it is an extremely powerful tool for improving image quality. The problem this creates is that the probe hardware is optimized for a single imaging system, i.e., one which has the correct number of system channels.
The current diagnostic imaging system requirements vary for different applications. For example, ultrasonic imaging systems may have any number of channels, e.g., 64 or 128. In order to maintain a family of diagnostic ultrasound transducers which can support these different imaging systems, a large number of probe types and the corresponding manufacturing burden are required. One method to decrease this manufacturing load is to provide a probe type which can be utilized for a family of imaging systems having different channel counts.